Steering columns for motor vehicles comprise a steering shaft with a steering spindle, on the rear end of which in a direction of travel, which end faces toward the driver, there is mounted a steering wheel for the introduction of a steering demand by the driver. The steering spindle is mounted rotatably in an adjustment unit which is mounted on the vehicle body by means of a support unit, which support unit, for the connection to the vehicle body, comprises for example bracket parts which hold the adjustment unit. Adjustable steering columns permit the adjustment relative to the vehicle body and thus an adaptation of the steering wheel position to the driver's position.
Adjustability in a longitudinal direction, that is to say in an axial direction of the steering spindle, for the longitudinal adjustment of the steering wheel may be realized by virtue of the adjustment unit being designed to be variable in length, for example by means of an arrangement of casing tubes which is telescopable in the longitudinal direction, as described in the prior art in, for example, DE 10 2014 101 995 A1 or DE 10 2008 005 256 B4. These disclose an adjustment unit with an inner casing tube which is mounted in an outer casing tube so as to be capable of sliding in an axial direction. For the adjustment in the direction toward the driver's position, the inner casing tube can be moved telescopically out of the outer casing tube, and correspondingly, for the adjustment in the direction away from the driver's position, said inner casing tube can be retracted into the outer casing tube.
It is known in the prior art, for the execution of the adjustment movement of the adjustment unit relative to the support unit, to provide a motor adjustment drive which comprises, for example, an electric motor which is coupled to the adjustment unit by means of a gear mechanism and which permits electrical control of the steering wheel positioning.
For the longitudinal adjustment, a linear motor adjustment drive is used between the inner and outer casing tubes. By means of the adjustment drive, the casing tubes can be moved in translational fashion relative to one another in the direction of the longitudinal axis, such that the inner casing tube is deployed or retracted in telescopic fashion relative to the outer casing tube. The adjustment drive may be realized for example by means of a spindle drive which comprises a spindle nut screwed onto a threaded spindle, which spindle nut can be driven in rotation relative to the spindle by an electric motor. For the function, it is essential here that the casing tubes can be moved freely relative to one another in both longitudinal directions, that is to say slide with adequately low friction, such that they can be moved reliably by the adjustment drive for the retraction and deployment.
An advantage of motor-adjustable steering columns lies in the increase in driving and operating comfort, for example by virtue of the fact that individual steering wheel positions for different drivers can be electronically stored and automatically retrieved and set when required. It is furthermore of particular interest for the steering column to be moved into predefined positions automatically in certain operating situations. For example, during autonomous driving during travel, no manual steering intervention by the driver is necessary, such that the steering wheel can in principle be stowed outside the operating position in order that the vehicle interior space thereby freed up can be put to alternative use. A stowable steering column of said type is described for example in DE 20 2014 101 156.
The known steering columns that can be longitudinally adjusted by motor means duly permit a shortening of the adjustment unit by retraction of the inner casing tube, such that, in the retracted state, space is freed up relative to the driver's position. It is however a disadvantage that the known steering columns either cannot be retracted far enough for stowage purposes, or comprise relatively large dimensions in a longitudinal direction in the retracted state in order to realize an adequate adjustment travel.
Thus a need exists for a motor-adjustable steering column that makes it possible to realize an increased adjustment range along with small dimensions in a retracted state.